Interleukin-2 (IL-2) is a lymphokine produced by T cells. IL-2 has a broad spectrum of growth and differentiation-promoting properties. Interleukin-2 enables T cells to grow for extended periods in vitro, enhances the immune response in animals against bacterial, parasitic, fungal, protozoan, and viral antigens, and promotes the differentiation and proliferation of killer cells. Administration of IL-2 in vivo enhances allogeneic responses and allows induction of cytotoxic and helper T cells in nude mice and chemically immunosuppressed animals. See, Journal of Immunology, 131:806 (1983); Journal of Immunology, 123:2928 (1979), Journal of Immunology, 130:222 (1983); and Immunological Review, 51:337 (1980).
Interleukin-2 was initially made by cultivating human peripheral blood lymphocytes or other interleukin-2 producing cell lines as disclosed in U.S. Pat. No. 4,401,756. However, because of difficulties in obtaining useful amounts, recombinant DNA techniques were developed to provide alternative methods for producing useful quantities of interleukin-2. Taniguchi et al., Nature 302:305-310 (1983) and Devos, Nucleic Acids Research 11:4307-4323 (1983) have reported cloning the human IL-2 gene and expressing it in microorganisms.
Subsequently, interleukin-2 analogs and derivatives having substituted, deleted, and added sequences were developed. These analogs possessed interleukin-2 activity and provided other advantages such as easier purification, easier administration, and the like. For example, Belgian Patent No. 898,016, granted Nov. 14, 1983 described muteins of IL-2 in which the cysteine normally occurring at position 125 of the wild-type or native molecule has been deleted or replaced with a neutral amino acid, such as serine. These muteins possess IL-2 biological activity. The Belgian patent states that the recombinant muteins may be formulated and administered as with native IL-2 by combining them with aqueous vehicles and injecting them intravenously, subcutaneously, or the like. U.S. Pat. No. 4,518,584 to Mark, incorporated herein by reference, discloses human recombinant IL-2 muteins having deleted or replaced cysteine residues. U.S. Pat. No. 4,508,833 to Sonneborn et al, incorporated herein by reference, reviews the methods for purifying IL-2 and discloses a purification method using dimatrix chromatography. The properties and function of IL-2 are reviewed in Smith, Immunological Reviews, 51:337 (1980).
FK-565 is a macrophage activator which is reported to increase host resistance to infection, induce interleukin-1 production in macrophages, and enhance phagocytic and killing activiries of macrophages. Agric. Biol. Chem., 48(9):2393-2394 (1984). FK-565 is a synthetic derivative of a natural peptide FK-156 isolated from the culture filtrate of strains of Streptomyces olivaceogriseus sp nov. and Streptomyces violaceus. The isolation, purification, and structure of FK-156 has been thoroughly reviewed in the literature: J. Antibiotics, 35:1280-85 (1982) (Taxonomy of the Producing Strains); J. Antibiotics, 35:1286-92 (1982) (Fermentation, Extraction and Chemical and Biological Characterization); J. Antibiotics, 35:1293-99 (1982) (Structure Elucidation); and J. Antibiotics, 35:1300-11 (1982) (Synthesis of FK-156 and Its Geometric Isomer). U.S. Pat. No. 4,311,640 to Kuroda et al, incorporated herein by reference, discloses methods for preparing FK-156 and some of its derivatives. U.S. Pat. No. 4,322,341 to Kitaura et al, incorporated herein by reference, discloses methods for producing FK-565. U.S. Pat. No. 4,349,466 to Kitaura et al, incorporated herein by reference, discloses methods for producing several immunostimulating peptides related to FK-565. ##STR1##
IL-2 and FK-565 are immunostimulants known to separately increase the immune system's response to invading antigens by stimulating a component of the immune system; IL-2 stimulates T cells, B cells, and macrophages and FK-565 stimulates macrophages and natural killer cells. However, the immune system's response to these and other immunostimulating agents is not always sufficient to protect the animal from disease, infections, antigens, trauma, and the like. There is, consequently, a continuing search in the art for new and better methods for stimulating the immune system. A method is, therefore, needed which can stimulate the immune system more effectively than previous immunostimulating methods and further increase the beneficial effect of immunostimulants on the immune system.